The purpose of this study was to clarify the following : 1) effect on the elasticity of the musculus trapezius caused by psychological load, and 2) relationship between psychological load, muscle elasticity, and the autonomic nervous system (ANS) by frequency analysis of heart rate variability.The experiment was conducted on a group of 30 healthy volunteers, consisting of 16 males and 14 females with an average age of 31.2 years old. We investigated and compared the changes in muscle elasticity and ANS in the case of control (resting), phonating and mental calculation as psychological load. Psychological status and stress response were measured by using State-Trate Anxiety Inventory (STAI), Stress Checklist (SCL), and Stress Tolerance Checklist (STCL) .As a result, the subjects experienced effective acute emotional stress during mental calculation, and muscle elasticity increased significantly.Heart rate (HR), low frequency (LF) component, and LF/HF increased significantly during mental calculations. The high frequency (HF) component tended to decrease during mental calculations.The rate of elevation of muscle elasticity and HR (difference between at rest and when calculating) was significantly related to STAI and STCL. STCL was significantly related to state of anxiety. The results of this study suggest that anxiety and stress tolerance affect muscle elasticity.